Corona discharge device

ABSTRACT

A corona discharge device for use in electrophotography and electrostatic printing apparatuses is provided having a corona discharge electrode, a shielding back plate with a corona discharge aperture and one or more conductive plates. Each of the conductive plates is insulated from the remainder of the apparatus and positioned adjacent to the aperture. A potential is impressed on each of these plates during corona discharge to prevent dust and other foreign particles from entering through the aperture and adhering to the electrode.

United States Patent Kamogawa et al.

[ Aug. 21, 1973 CORONA DISCHARGE DEVICE [75] Inventors: Nin-Ichi Kamogawa; Minoru Okumura, both of Tokyo, Japan [73] Assignee: Konishiroku Photo Industry Co.,

Ltd., Tokyo, Japan [22] Filed: Mar. 16, 1971 [21] Appl. No.: 124,696

[52] U.S. Cl. 250/326 [51] Int. Cl G03g 15/00 [58] Field of Search 250/49.5 ZC

[56] References Cited UNITED STATES PATENTS 3,339,069 8/1967 Hayne 250/49.5 ZC 3,496,352 2/1970 Jugle 250/49.5 ZC

Primary ExaminerJames W. Lawrence Assistant Examiner-C. E. Church Attorney-Harry C. Bierman, Jordan B. Bierman and Bierman & Bierman [57] ABSTRACT A corona discharge device for use in electrophotography and electrostatic printing apparatuses is provided having a corona discharge electrode, a shielding back plate with a corona discharge aperture and one or more conductive plates. Each of the conductive plates is insulated from the remainder of the apparatus and positioned adjacent to the aperture. A potential is impressed on each of these plates during corona discharge to prevent dust and other foreign particles from entering through the aperture and adhering to the electrode.

6 Claims, 6 Drawing Figures I I I Ink Patented Aug. 21, 1973 v 3,754,137

2 Sheets-Sheet l M /au/a qw 7/1 Z INVENTOR ATTORNEYS Patented Aug. 21, 1973 2 Sheets-Sheet 3 Fig.5

MIh/c/v, a mogaw {/Ff/ura akwmm INVENTORY ATTORN EYS CORONA DISCHARGE DEVICE The present invention relates in general to a corona discharge device, and more particularly to an improvement in a corona discharge device for use in an electrostatic photography or electrostatic printing.

Heretofore, the art of electrostatic photography has been known and commonly practiced, in which a sheet of electrophotographic sensitive paper supported on a conductive back plate is passed across an elongated gap of a corona discharge device in a closely separated relation therefrom so that the exposed surface of said sensitive paper may be uniformly charged, and then said surface is exposed to an optical image of a pattern to be photographed. Thereafter, an electrostatic latent image produced on said sensitive paper is developed by means of toner powders into a visual image, said visual image being transferred onto a separate sheet of paper superposed thereon while being subjected to corona discharge by means of another corona discharge device disposed on the backside of said separate sheet at a position remotely located from said first corona discharge device, and finally the transferred visual image on said separate sheet is fixed with a heater device, while the surface of the original electrophotographic sensitive paper is cleaned with a cleaner device so as not to retain the toner powders thereon at all for allowing the same original sensitive paper to be reused in the next electrophotographic operation.

In the aforementioned type of electrophotographic apparatus including a powder developer and corona discharge devices, the developer powder, i.e., the toner and other dust or foreign matters are apt to adhere to a corona discharge electrode wire, and the toner, dust, etc., adhered to the wire causes decrease of the discharging rate or stoppage of the discharge.

In case that the corona discharge device is employed as a charging device for the electrophotographic sensitive paper in the electrophotographic apparatus, even if the amount of the toner or the like adhered to the discharge electrode wire should be extremely small, it would result in unevenness of the corona discharge current density which badly affects upon the quality of the finally obtainable picture image.

More particularly, the difference in the produced corona discharge current density between a part of the corona discharge device where the toner or the like adheres to the discharge electrode wire and another part thereof where the toner or the like does not adhere to the wire, results in a difference in the sensitivity between the corresponding surface regions on the electrophotographic sensitive paper passing beneath the corona discharge device, so that even if said sensitive paper were to be subjected to the same exposure and the same develop processing, an equal density could not be obtained and thus light and shade would appear in the picture image.

In addition, in case that the corona discharge device is employed as a transfer device for transferring the visual image on the original sensitive paper sheet onto the other paper sheet, also a bad effect upon the picture image is found due to the adhesion of the toner or the like to the corona discharge electrode wire, although there may be some difference in extent from the case of the charging device.

The principal source which produces the toner or the like adhering to the discharge electrode wire, is the developer device and the cleaner device such as a cleaning brush, and the toner produced in this developer consists of powders charged either positively or negatively, said polarity being opposite to the polarity of the discharge electrode, and therefore, the toner is extremely liable to adhere to the corona discharge electrode wire owing to a Coulomb force.

On the other hand, the corona discharge device produces a wind outwardly of said device which is induced by a corona discharge current directed to the surface of the electrophotographic sensitive paper, and accordingly, another wind directed to the interior of the device is produced at a separate portion of the corona discharge device in order to necessarily compensate for said wind. Due to the wind directed to the interior of the device, the adhesion of the toner or the like to the discharge electrode wire may be further promoted.

Electrophotographic copying machines in the prior art were not provided with means for effectively preventing such adhesion of the toner to the discharge electrode wire, and so said electrophotographic copy"- ing machines had a remarkable disadvantage from a practical point of view.

The present invention has been proposed in order to overcome the above-mentioned disadvantages of the corona discharge device in the prior art to be used in an electrophotographic machine, andone object of the present invention is to provide a novel corona discharge device in which the adhesion of the toner or the like to the discharge electrode wire may be prevented, whereby a reproduced picture image of excellent quality maybe obtained and also the life of said device may be prolonged.

One feature of the present invention is the provision of a corona discharge device for use in an electrophotographic apparatus consisting of a corona discharge electrode and a shielding back plate having a corona discharge aperture and disposed surrounding said corona discharge electrode, characterized in this that at a position in the proximity of said discharge aperture is provided a conductive plate for preventing dust, which is electrically insulated from said back plate and other portions of said apparatus.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view for explaining a typical electrophotographic process in which the corona discharge device according to the present invention is to be employed.

FIG. 2 is a schematic cross-section view'of one preferred embodiment of the present invention,

FIG. 3 is a schematic cross-section view of a-modified embodiment of the present invention,

FIG. 4 is a perspective view partially cut away of another embodiment of the present invention,

FIG. 5 is a schematic cross-section view of the embodiment in FIG. 4 taken along line A-A' as viewed in the direction of arrows, and

FIG. 6 is a schematic cross-section view of still another embodiment of the present invention.

At first, for the purpose of facilitating to understand the function, effect and advantage of the corona discharge device according to the present invention when it is employed in an electrophotographic apparatus, a common electrophotographic apparatus will be explained with reference to FIG. 1 of the drawings. In this figure, reference numeral 1 designates a drum rotating at a predetermined angular velocity in the direction shown by an arrow A, and reference numeral 2 designates an electrophotographic sensitive paper sheet which consists of insulating photoconductive material coated on a conductive supporting base.Reference numeral 3 designates a charging device which makes use of a corona discharge, and reference numeral 4 designates a lens which symbolically represents the optical system for projecting an image of an original picture onto the sensitive paper sheet 2. Reference numeral 5 designates a developer device comprising a developing brush, that is made of a rotating magnet having a developing agent consisting of a mixture of toner and iron powders adhered thereto, and since the polarity of the electric charge borne on the toner is selected to be opposite to that of the electrostatic latent image retained on the sensitive paper sheet 2, the toner is attracted by the electrostatic image on the sensitive paper sheet, and thereby the latent image can be visualized. Reference numeral 6 designates a transfer paper sheet supplied in synchronism with the drum 1, which travels in the direction shown by an arrow B and is superposed onto the sensitive paper sheet 2 at a location just above a transfer device 7 which also consists of a corona discharge device, and thereby the toner picture image borne on the surface of the sensitive paper sheet 2 may be transferred to the side of the transfer paper sheet. Reference numeral 8 represents a belt for advancing the transfer paper sheet 6, which is separated from the sensitive paper sheet 2 at a location where the belt 8 makes contact with the circumferential surface of the drum 1, and then advanced along the belt 8.1Reference numeral 9 designates a thermal fixing device, and a lamp l0 and a brush 11 form a cleaner device which serves to remove the toner remaining on the sensitive paper sheet 2 so as to enable the sensitive paper sheet 2 to be reused in the next copying process.

The corona discharge device according to the present invention can be employed as the corona discharge device 3 and 7 in the above exemplified electrophotographic apparatus.

It is a matter of course that the corona discharge device according to the present invention can be employed equally to other apparatuses such as an electrostatic printing apparatus.

Now, the present invention will be described in connection to its preferred embodiments illustrated in FIGS. 2 to 6 of the accompanying drawings.

Referring to FIG. 2, reference numeral 12 designates an electrophotographic sensitive paper sheet supported on a conductive supporting base 13, numeral 14 designates a corona discharge electrode wire, numeral 15 designates a shielding back plate made of conductive material such as metals, numeral 16 designates an insulative plate for insulating the back plate 15 from a conductive plate 17 which is provided for preventing dust, and numeral 17 designate said conductive plate made of metal or the like and having a L-shaped crosssection. This conductive plate 17 is insulated not only from the back plate 15 but also from other mechanical parts of the apparatus. Reference numeral 18 designates an electric power supply for applying a high voltage required for the corona discharge to the discharge electrode wire 14. In the illustrated embodimennthe discharge electrode wire 14 is applied with a negativ voltage. t

A corona discharge occurs between the discharge electrode wire 14 and the conductive supporting base 13, and thereby the surface of the sensitive paper sheet 12 is charged with a negative charge.

Upon this corona discharge, a part of the discharging current flows to the conductive plate 17 though only a very little. Especially, it is to be noted that this current flows only during the very initial short period of time upon discharge. Inasmuch as the conductive plate 17 is insulated from the back plate 15 as well as other mechanical parts of the apparatus as described above, a negative potential appears at the conductive plate 17 owing to the corona current. The magnitude of the potential appearing at the conductive plate 17 can be varied depending upon the respective positions of the back plate 15, the insulative plate 16, the conductive plate 17, etc., the distance between the respective members, the dimensions of the respective members, and the magnitude of the applied voltage.

In the case of an apparatus, in which the sensitive paper sheet 12 is charged with a negative charge as shown in FIG. 2, generally the toner has a positive polarity in the developing stage.

While an air flow containing the toner produced at the developer device, the cleaner device and other various mechanical parts is likely to enter the interior of the corona discharge device throughthe gap space between the conductive plate 17 and the sensitive paper sheet 12, the toner is attracted by the conductive plate 17 due to an electric field generated between the sensitive paper sheet 12 and the conductive plate 17 which is negatively charged as described above, so that only a clean air flow can enter the interior of the corona discharge device. In other words, the toner is blocked from entering the interior of the corona discharge device owing to the curtain of electric field generated between the conductive plate 17 and the sensitive paper sheet.

In this case, the sensitive paper sheet 12 is caused to continuously travel across the discharge aperture of the corona discharge device just beneath the same, and thereby an electric charge is uniformly applied onto the surface of the sensitive paper sheet 12. Accordingly, at the portion of the sensitive paper sheet 12 located just beneath either one of the left and right conductive plates 17, there exists a negative surface potential. Preferably, if the arrangement of the respective parts is selected such that the absolute value of the potential at the conductive plate 17 may become larger than the absolute value of the surface potential on the sensitive paper sheet whether the potentials are both positive or negative, then the blocking effect by means of the curtain of electric field can be maintained.

Although most of the particles of the toner, dust, etc., are charged positively as described above, particles having an opposite, i.e., negative polarity of electric charge are also contained therein at a certain proportion. Such toneigdust, etc. are, oppositely, repulsed and rejected by the conductive plate 17, and thus they are prevented from entering the interior of the corona discharge device.

As described, according to the present invention, the harmful charged particles such as toner, dust, etc., can be prevented from entering the interior of the corona discharge device by the provision of the conductive plate 17 as well as the generation of D.C. potential at said conductive plate 17, whether said potential is positive or negative with respect to the potential at surface of the photographic sensitive sheet 12, in the former case positively charged particles being blocked by repulsion, while in the latter case the positively charged particles being blocked by attraction.

According to one embodiment of said former type, when the corona discharge voltage was selected at -6 KV, the gap distance between the conductive plate 17 and the sensitive paper sheet 12 being chosen equal to 2 mm, the thickness of the insulative plate 16 being chosen equal to 0.5 mm, a voltage equal to 240 V being generated at the conductive plate 17 on the inlet side for the sensitive paper sheet, and the conductive plate 17 on the outlet side for the sensitive paper sheet was grounded, a favorable result was obtained. More particularly, in contrast to the fact that according to the electrophotographic copying process by means of the corona discharge device in the prior art, at the stage where about 4,000 sheets of copy had been reproduced, a fault occurred in the generation of corona due to the adhesion of the toner or the like to the discharge electrode wire, and thus cleaning of the corona discharge device was necessitated; in the case of the corona discharge device according to the present invention, even after 16,000 sheets of copy had been reproduced, the fault in the generation of corona could not be found.

It is to be noted that since the corona current flowing to the conductive plate 17 is an extremely small fraction with respect to the entire corona current, and also since said current flows only during the very initial period of discharge, the effect upon the corona discharge current flowing to the sensitive paper sheet 12 of the provision of the conductive plate 17, is negligibly small.

FIG. 3 shows an alternative embodiment, in which the arrangement is such that the lower end portions of the L-shaped conductive plates 17 are located lower than the lower end portions of the back plate and the insulative plates 16. According to this embodiment, when the corona discharge voltage at the power supply 18 was maintained at 6000 V, a voltage of 800 V was obtained at the conductive plate 17, and an excellent dust blocking effect for the discharge electrode wire 14 could be obtained. In this embodiment also, the effect upon the corona discharge current flowing from the discharge electrode wire 14 to the sensitive paper sheet 12 of the provision of the conductive plate 17, was negligibly small.

FIGS. 4 and 5 show still another embodiment of the present invention, in which the arrangement is such that a portion of the back plate 15 and the insulative plate 16 is cut away slightly in the proximity of an insulative block 19 which is not used for the charging of the sensitive paper sheet 12, and a conductive charge absorbing plate mounted on the conductive plate 17 is exposed towards the interior of the discharge device through said cut away portion along the same plane as the inner surface of the side wall of the back plate 15. According to this embodiment, when the corona discharge voltage at the power supply 18 was maintained at 6000 V, the voltage generated at the conductive plate 17 rised up to 2000 V. In this case also, the effect upon the corona discharge current flowing from the discharge electrode wire 14 to the sensitive paper sheet 12 of the provision of the conductive plate 17 as well as the conductive charge absorbing plate 20, was negligibly small.

As described above, it will be readily appreciated that since the provision of the electrical dust blocking conductive plate 17 in the proximity of the aperture of the corona discharge device according to the present invention can affect upon the corona discharge current flowing from the discharge electrode wire 14 to the sensitive paper sheet only to a negligibly small extent, the corona discharge device per se, except for the insulative plate 16 and the conductive plate 17, may be designed in the manner most suitable for its purpose just as done in the past.

FIG. 6 shows yet another embodiment of the present invention, in which the basic construction consisting of the back plate 15, the insulative plate 16 and the conductive dust blocking plate 17 is similar to the abovedescribed embodiments. However, this embodiment is characterized in that the conductive plate 17 is applied with a D.C. voltage that is far lower than the corona discharge voltage at the power supply 18 by means of a separate power supply 21, to generate the curtain of electric field. According to this method for applying a voltage to the conductive electrode 17, also the effect upon the corona discharge current flowing from the discharge electrode wire 14 to the sensitive pape sheet is negligibly small, just as the preceding embodiments. However, according to this method for application of a voltage to the conductive plate 17 if necessary, it is also possible to apply to the conductive plate 17 a D.C. voltage in the opposite polarity to the corona discharge voltage, or to apply an AC. voltage thereto. Furthermore, it is also possible to provide double layers of conductive plates 17 and to operate the device while applying a same polarity of voltage as the corona discharge voltage to one of the conductive plates 17 and an opposite polarity of voltage to the corona discharge voltage to the other of the conductive plates 17.

While an insulative plate 16 is interposed between the back plate 15 and the conductive plate 17 in the above-described embodiments, it is a matter of course that nothing may be interposed between the back plate 15 and the conductive plate 17, and the space therebetween may be kept vacant. In this case, the conductive plate 17 must be fixedly secured to a portion of the apparatus'by means of any insulative member.

In addition, inasmuch as the dust blocking plate 17 is conductive, it is only necessary that at least a certain portion of said plate can absorb the corona charge. Therefore, the dust blocking plate 17 is, of course, not limited to the physical configurations as illustrated in the above-described embodiments, but it can be extended to and disposed at any location where it is necessitated for dust blocking, within the region where it affects only negligibly upon the corona discharge current flowing from the discharge electrode wire 14 to the sensitive paper sheet 12.-

Furthermore, in case that the apertures of the corona discharge device are provided at two or more locations of the device, also the dust blocking plates 17 are, of course, disposed in the proximity of the respective apertures according to the requirement.

Because of the aforementioned constructions, the corona discharge device according to the present invention can effectively prevent thefloatirig toner, dust, foreign matters, etc., from adhering to the corona discharge electrode wire by means of a simple structure, and thus it enables to obtain a picture image of excellent quality when employed in an electrophotographic apparatus, and further the present invention can prolong the life of the corona discharge device. Therefore, the present invention is practically very useful.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim;

1. A corona discharge device for use in electrophotographic and electroprinting apparatus of the type having insulating photoconductive material comprising corona discharge electrode means, a shielding member comprising grounded conductive material surrounding said corona discharge electrode means, said grounded conductive material having an aperture therein to permit corona charging of said insulating photoconductive material, at least one conductive plate insulated from the corona discharge device, said at least one conductive plate being positioned adjacent to said aperture parallel to and in electric field forming relationship to said insulating photoconductive material, said at least one conductive plate having a sufficient D.C. potential impressed thereon during corona discharge such that said field is sufficient to prevent the entry of dust and foreign particles through said aperture.

2. The apparatus specified in claim 1 further comprising D.C. power supply means connected to said at least one conductive plate for supplying said D.C. potential.

3. The apparatus specified in claim 1 further comprising a plurality of said conductive plates.

4. The apparatus specified in claim 1 further com prising insulating material mounted between said at least one conductive plate and said shielding member.

5. The apparatus specified in claim 1 wherein said D.C. potential is impressed on said at least one conductive plate by the corona discharge electrode when operating in the discharge mode.

6. The apparatus specified in claim 1 wherein said at least one conductive plate is positioned outside said aperture. 

1. A corona discharge device for use in electrophotographic and electroprinting apparatus of the type having insulating photoconductive material comprising corona discharge electrode means, a shielding member comprising grounded conductive material surrounding said corona discharge electrode means, said grounded conductive material having an aperture therein to permit corona charging of said insulating photoconductive material, at least one conductive plate insulated from the corona discharge device, said at least one conductive plate being positioned adjacent to said aperture parallel to and in electric field forming relationship to said insulating photoconductive material, said at least one conductive plate having a sufficient D.C. potential impressed thereon during corona discharge such that said field is sufficient to prevent the entry of dust and foreign particles through said aperture.
 2. The apparatus specified in claim 1 further comprising D.C. power supply means connected to said at least one conductive plate for supplying said D.C. potential.
 3. The apparatus specified in claim 1 further comprising a plurality of said conductive plates.
 4. The apparatus specified in claim 1 further comprising insulating material mounted between said at least one conductive plate and said shielding member.
 5. The apparatus specified in claim 1 wherein said D.C. potential is impressed on said at least one conductive plate by the corona discharge electrode wheN operating in the discharge mode.
 6. The apparatus specified in claim 1 wherein said at least one conductive plate is positioned outside said aperture. 